Signaling system for transformers



Oct. 6, 1942- J. K. HODNETTE SIGNALING SYSTEM FOR TRANSFORMERS FiledAug. 5, 1940 INVENTOR 200.551.) Cal/A650 WITNESSES:

Patented Oct. 6, 1942 SIGNALING SYSTEM FOR TRANSFORMERS John K.Ho'dnette, Sharon, Pa., assignor to Westinghouse Electric &Manufacturing Company, East Pittsburgh, Pa., a corporation ofPennsylvania Application August 3, 1940, Serial No. 350,381

Claims.

The invention relates to a light signaling system for transformers.

In the usual power and light distribution systerns employed forsupplying cities and rural sections, innumerable distributiontransformers are located'at different points throughout the areassupplied. The loads imposed on these distribution transformers locatedat a distance from the power stations fluctuate continuously withchanges in demands in the different localities.

In order to ascertain whether or not a particular transformer is beingsubjected to an overload, it has been necessary in the past to send outservice men with graphic instruments to measure the load. Theapplication of the instruments is usually rather difllcult, and thereading of the instruments consumes time, thereby making the methodexpensive. Further, in order to have good records, it is necessary totest all transformers at short intervals, which greatly increases theservice charges.

The usual practice when designing distribution systems is to providetransformers with excess capacity in order to provide for futureincreases in load. In many instances, this results in unnecessaryexpenditures in equipment and greatly increases the overhead expense.Even with this excess capacity, transformers are often excessivelyloaded with the result that they may be burned out and the serviceinterrupted. This is expensive and brings complaints from customers.

It is the object of the invention to provide a source of energy forilluminating a signal lamp associated with a transformer withoutsubjecting the signal lamp to any appreciable surge current which mightcause a burnout as the result of lightning disturbances on thedistribution system.

Other objects of the invention will, in part, be obvious, and, in part,appear hereinafter.

The invention, accordingly, is disclosed in the accompanying drawing andcomprises the features of construction, combination of elements andarrangement of parts which will be exemplifiedin the structurehereinafter set forth and the scope of the application of which will beindicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference may be had to the following detailed description taken inconnection with the accompanying drawing in which:

Figure 1 is a view in section showing how the signal coil is disposed onthe transformer core and. insulated from the transformer windings, a d

Fig. 2 is a diagram of the circuit connections of the transformershowing how the coil for supplying the signal lamp is disposed withrelation to the core and windings of the transformer.

With the advent of the completely self-protecting transformers such asdisclosed in the applicants Patent No. 2,066,935, issued January 5,1937, an effort was made to provide a visual signal which would functionin conjunction with the protecting apparatus to indicate when atransformer had been subjected to overload conditions. The intention wasto provide a signal lamp which would be connected across a source ofpower to illuminate it when the transformer was subjected to overloadconditions which were greater than the rated capacity of the transformerbut less than the overloading required to operate the apparatus providedfor disconnecting the transformer from the system. The provision of apower source for illuminating the signal lamp became a problem.

To provide a source of power other than the transformer would be veryexpensive and probably more burdensome than to provide the excesstransformer capacity aswas the practice in the older distributionsystems. It became apparent that the only economical and sound method ofproviding a source of supply for th lamp was to utilize the transformeritself, in some way, to provide the necessary current.

The obvious thing to do would be to utilize the low-voltage winding ofthe transformer for the source of energy for the signal light. Wherethis was tried, it was found that the signal lamp was vulnerable tosurges imposed on the line as a result of electrical disturbances of onekind or another.

These surges imposed a voltage across th low voltage winding comparablein magnitude to the surge voltage on the system. When the signal lamp isconnected across the low voltage winding it is actually a low resistancecircuit connected in parallel with an inductive member and the result isan initial high current flow through the signal lamp.

Attempts to utilize a low-voltage lamp which would have acorrespondingly large filament supplied by taps taken from the windingas near the grounded end as possible were also unsuccessful. Even underthis condition the'surge current conducted through the lamp was found tobe sufficient to burn out the lamp filament in spite of its greatercross-section.

In Patent No. 2,223,530, issued December 3, 1940, and assigned to theWestinghouse Electric visible signal when the transformer was subjectedto an overload.

Facing these difliculties, the present applicant conceived the idea ofproviding a separate coil of few turns disposed on the transformer corein such position as to be only loosely coupled, to the other,transformer windings. This arrange ment proved effective since the loosecoupling does not transmit the full inductive effect of the lightningsurge, and it wasfound that even in the case of severe lightningstrokes, no damage resulted to the signal-lamp filament.

The next step was the matter of designing the signal-lamp coil with theproper number of turns for the rating of the transformer or the systemwith which it was to be utilized and so disposing the coil as to preventthe flow of surge current through it. This requires that there be nometallic connection between the low-voltage windings of the transformerand the signal-light coil.

Referring now to Fig. l in particular, a standard type of transformer Iis illustrated. The transformer comprises a core H provided with alow-voltage winding [2 disposed between the usual low-voltage andhigh-voltage barriers I 3 and M, respectively. The low-voltage windingI2 is wound on the core II in the usual manner.

In accordance with my invention an auxiliary winding or coil l 5,provided for supplying the si nal lamp I6, is inductively disposed onthe leg of the core I I, and located near one end of the leg. Asillustrated, the coil I5 is separated from the low voltage winding l2 byspacers l1 and a Fuller board channel l8. The Fuller board channel isprovided with an offset which extends partially around the coil l5. ThisFuller board channel extends alongside of the yoke l9 of the core.

In this particular embodiment of the invention the coil I 5 is separatedfrom the core-iron by means of a layer of paper 20. As illustrated, thepaper 20 is bent at right angles to' separate the coil l5 from the legand the yoke of the core I l. The high voltage winding 2! is also spacedfrom the coil 15.

The size of the barrier II, the thickness of the Fuller board channelI8, and the thickness of the paper layer 20 will all depend upon thetransformer for which the coils are designed. It will be noted that thelow-voltage Winding l2 has been shortened to accommodate the mounting ofthe signal-lamp coil l5 on the leg of the core H. While this shorteningof the low-voltage winding did not at first seem to be altogetherdesirable; from the standpoint of the ordinary design and operation ofthe transformer, it has been found that a transformer can be designed soas to render this slight change in the design of the low-voltage windingl2 immaterial. It was found in practice, in the year 1939, that thischange after all involve no appreciable disadvantage in the constructionand operation of the transformer. When the coil I5 is mounted in themanner described, that is, spaced from the primary and secondarywindings it is substantially unaffected by surge voltages impressed onthe transformer windings but it will impress on the lamp IS a voltagewhich has a predetermined reiation to the rated voltage of thetransformer.

The completely self-protecting transformer disclosed in applicantspatent identified hereinbefore was received by the trade as being quiterevolutionary in the transformer art. An extensive installation wasmade, but to the great disappointment of those concerned, the signallamps which were mounted in the transformer were grammatic showing,switching-means shown generally at 22 are shown for connecting the lampl6 across the coil I5. While various types of switching apparatus may beemployed for this purpose, it is preferred to utilize the apparatusprovided in conjunction with the completely selfprotecting transformerand which is shown and described in the Patent 2,223,530, issuedDecemher 3, 1940, hereinbefore referred to.

This apparatus, provided for disconnecting the transformer from theline, connects the signal lamp across the coil when a predeterminedoverload is imposed on the transformer. The signal lamp is so disposedthat it can be readily observed from the ground, and a service man whomakes regular rounds can easily see from a distance Whether or not thetransformer has been subjected to an overload. If he suspects that theoverload is of a temporary nature, he may reset the apparatus asdescribed in the application referred to, and if the signal lamp is soonre-lighted, then it is evident that the transformer is beingcontinuously overloaded.

When the breaker illustrated schematically in Fig. 2 stands closed, thecontact members 23 and 24 stand in spaced relation as illustrated. Ifthe transformer is overloaded, the bimetal 9 raises the latch 25 and thedog 26 is. actuated by the spring 27 to close the switch 22. A lightingcircuit is established which may be traced from one side of coil l5through the lamp l6, conductor 28, contact members 23 and 24, switch arm32, conductors 29 and 30, back to the coil IS. The lamp 15 will beilluminated for signaling purposes.

In this manner the operating staff of any distribution system is madeaware of the fact that the transformer is not of suificientcapacity forthe locality in which it is located and that a transformer of greatercapacity should be sup plied.

By employing the completely self-protecting transformer and a signallight supplied by the applicants coil, a great saving in the initialinstallation costs of a distribution system may be made. It is notunusual to make installations in which apparatus of 20% smaller capacitymay be safely employed without any serious interruptions in service.This signaling system has made it possible to eliminate almostcompletely the previous practice of checking loads with graphicinstruments.

In some instances, the oil will be disposed on only a portion of themagnetic core. A good example is in the case of large transformers whereeven one turn in the signal coil would give a voltage in excess of therated voltage of the signal lamp. The core may also be slotted toreceive the coil l5.

In conclusion, it is pointed out that, while the illustrated exampleconstitutes a practical embodiment of my invention, I do not limitmyself to the exact details described, since the materials may beconsiderably varied without departing from the spirit of the inventionas defined in the appended claims.

I claim as my invention:

1. In a light-signaling system for a transformer provided with a coreand high-and low-voltage windings, in combination, an electric lamp forgiving a visible signal when predetermined load conditions develop, acoil for supplying electric current to the lamp, means responsive toload conditions for connecting thelamp to the coil, the coil being sospaced from the transformer windings that substantially no change involtage across the lamp results from the surges impressed on thetransformer windings and so looped around the core that it will impressa predetermined voltage on the lamp when the transformer is subjected toload conditions which efiect the operation of the connecting means.

2. In a light-signaling system for a transformer provided with a coreand high and low voltage windings, in combination, an electric lamp forgiving a visible signal when predetermined load conditions develop, acoil for supplying electric current to the lamp, a switch responsive toload conditions for connecting the lamp to the coil, the coil being sodisposed on the core that there is no metallic connection with thewindings, and loose electrostatic and electromagnetic connections withthe windings permitting leakage whereby the coil and therefore the lampis substantially unaffected by surges impressed on the transformerwindings.

3. In a light-signaling system for a transformer provided with a coreand main transformerwindings, in combination, an electric lamp forgiving a visible signal, and a lamp-energizing means including a coildisposed on the core in such position as to have loose electrostatic andelectromagnetic couplings to the main transformer-windings whereby thecoil and lamp are substantially unaffected by surge voltages impressedon the transformer windings.

4. In a light-signaling system for transformers provided with cores andhigh and low voltage windings, in combination, an electric lamp forgiving a visible signal when predetermined load conditions develop, acoil for supplying electric current to the lamp, a circuit breakerdisposed to connect the lamp across the coil, the coil being so spacedfrom the transformer windings that it is substantially unaffected bysurges impressed on the transformer windings and so coupled with thecore that it will impress a voltage on the lamp which has apredetermined relation to load conditions.

5. In a light signaling system for a transformer provided with a coreand primary and secondary windings, in combination, an electricallyoperated lamp for giving a visible signal, a coil for energizing theelectrically operated lamp, the coil being looped around the core, thecoil being spaced from the primary and secondary windings, andinsulation barriers disposed between the coil and the primary andsecondary windings, the insulation and the spacing of the coil from theprimary and secondary windings being of predetermined dimensions wherebywhen surge voltages are impressed on the primary and sec ondary windingsthe inductive effect on the coil is so small that there is substantiallyno increase in voltage across the lamp.

JOHN K. HODNE'ITE.

